I didn't actually know until recently that Harmonium hadn't really sold well, and I was totally suprised tbh. I pre-ordered it on Amazon.com so I could get it when it first came out (the UK release date was quite a while later I think), and it was well worth the extra money (well ,my sister's extra money, it was released just before my Birthday so it didn't cost me lol). I thought the album was phenomonal, and equally as good if not better than BNN, which is pretty rare as many artists often produce pretty disappointing follow albums if their first was particularly good.
I can't believe it didn't sell more copies as it is so good, I think a lot of people probably don't know about it, especially outside of the US. Fortunately I checked her website a little before Harmonium's release, otherwise I don't think I would have even known about it.
Count yourselves lucky to have got one single, I don't even think White Houses was released in the UK lol